It’s my understanding that where a rotating part (e.g. a balance staff) and a stationary part (e.g. a plate bearing) mate, friction causes wear. Friction is a function of the smoothness of the parts and the pressure with which they mate. Wear on a part is reduced as its surface is made harder. When harder and softer parts mate the softer part is most likely to yield.

Many watches have jewel bearings (harder) instead of metal bearings (softer) to reduce wear on the bearings. Do you observe correspondingly more wear on the staffs? Or are jewel bearings enough smoother than metal bearings that wear on the staffs is also reduced?

[This message was edited by Dog on June 02, 2003 at 10:24.]

Dog,

I am often amazed at how long some watches will run, bone dry, without showing noticeable wear on certain parts that are equipped with jewelled bearings. Of course, while many of the jewelled bearings on a neglected watch soldier on, the metal to metal parts are wearing perceptibly. And even some jewelled parts such as rotor bearings (as in Rolex). Keeping the parts that are more susceptible to wear lubricated by regular servicing doesn't STOP wear on suceptible bearings, it just slows it down. And, of course, while all this is going on, the time keeping performance of the watch suffers.

Doug S.

Dog,

I had to replace a center wheel arbor on an old 15J, 18s gilt Elgin full plate. Although the unjeweled pivot hole had slight wear, the center wheel pivot (steel) was severely worn. I believe the pillar plate was made from nickel or a nickel alloy. In this case, the softer metal of the pillart plate seemed to wear better than the steel pivot.

John D. Duvall
Rosamond, CA.
NAWCC Member 0144772
NAWCC IHC Happy Camper 192

HI. I suppose the same rules apply in watches as in clocks, It is well known fact and commonly witnessed, in clocks the brass escapement wheel wears grooves in the hardened steel pallets, also steel pivots often wear, running in brass pivot holes.
Reason being dust and fine particles of grit imbed in the softer material and form an abrasive wearing/bearing surface. Regards, Ged.

Ged,

Thank you for explaining that. It makes total sense and also adds to the importance of regular movement cleaning and oiling.

John D. Duvall
Rosamond, CA.
NAWCC Member 0144772
NAWCC IHC Happy Camper 192

A similar situation often arises in two-tone gold & stainless watch bracelets. While the stainless parts are much harder, the wear on them after a number of years is often more severe than that on the softer gold parts.

The reason is exactly the same as that which allows a copper disk impregnated with diamond particles to cut through a block of solid granite. It's really the particles that are doing the cutting (or causing the wear) -- the soft metal is just holding them in place.

In the case of jewels and pivots, a pivot can run dry in a hole for a long time, as long as there isn't much pressure on it. It's always the high pressure pivots that begin to wear first when dry, and the evidence of that is a brown powder that's is commonly called "friction rust."

When pivots are running in non-jeweled holes, it's often the 4th wheel pivots that wear most rapidly. I'm sure that's a function of physics whereby wear is proportional to force multiplied by motion, but it would take someone smarter than I am to fully explain it.

As for the original topic, essentially, jewels are too hard to be worn BY the pivots, and too smooth to cause significant wear TO them, but obviously, keeping the pivots lubricated will extend their life, regardless of the type of hole they're running in.

====================

Steve Maddox
President, Chapter #62
North Little Rock, Arkansas

Off the subject but, look at crankshaft seals. That little leather or rubber seal lip wears a groove in that hardend bearing surface. Weird huh?

Aaron Bereiter
NAWCC# 156432
Chapter 185 Charter 23
Chapter 185 Finance VP
God bless America